The invention relates in general to a receiver for security systems which allows operation upon the receipt of a properly coded signal. More particularly, the invention relates to a digital super-regenerative receiver for a security system or to a barrier operator system, such as a garage door operator, employing a transmitter and a receiver.
It is well-known to provide radio-controlled garage door operators which include a garage door operator unit having a radio receiver and a motor connected to be driven from the radio receiver. The radio receiver is adapted to receive radio frequency signals or other electromagnetic signals having particular signal characteristics which, when received, cause the door to be opened. More recently, such transmitter and receiver systems have become relatively more sophisticated in that they use radio transmitters which employ coded transmissions composed of pulse width modulated signals to which may be assigned multiple three-values (0, 1 and 2), also known as "trinary bits" or other serial coded transmission techniques. Once such signals are received, a microcontroller is generally used to decode the trinary word.
Analog super-regenerative receivers have been known for use in such systems. Super-regeneration is a form of regenerative amplification. In a regenerative receiver, a detector is provided having positive or regenerative feedback from the output to the input. The feedback must maintain operation of the oscillator on the verge of oscillation. In a super-regenerative detector, the circuit is switched into and out of oscillation by an oscillator operating at a very low frequency rate, called the "quench" frequency. The quench frequency is lower than the carrier frequency but higher than the frequency of the modulating signal. That is, the oscillator allows oscillations to build up in the regenerative circuit and then causes them to die out.
In the absence of an incoming signal, oscillations are initiated by thermal noise, build up to a critical amplitude and die out. An incoming signal larger than the thermal noise advances the build up time. Thus, the peak is reached sooner, and the oscillations die out sooner. The frequency of interruption increases with signal strength. A detector will provide indication of the incoming signal based on the advance of the build up period.
Super-regenerative receivers provide greater sensitivity than other types of receivers. However, most analog super-regenerative receivers require a large number of analog components that are not easily integrated or incorporated into an application-specific integrated circuit (ASIC). As such, manufacturing costs are relatively high. In addition, such super-regenerative receivers require relatively high current to operate. Thus, they consume more power and decrease battery life. In addition, such super-regenerative receivers do not generally decode trinary word encoded signals themselves. Rather, a separate microcontroller is used, which must be kept constantly on. Even if the microcontroller is maintained at a lower-running clock speed, it will still draw current and hence decrease battery life. Also, many super-regenerative receivers require an audio amplifier, thereby increasing system complexity, cost and power consumption. Finally, many super-regenerative receivers are sensitive to variations in transistor characteristics.
Accordingly, there is a need for a relatively simple super-regenerative receiver that requires relatively low current and hence draws less power than previous receivers. There is a further need for a super-regenerative receiver that tracks the received signal more quickly than other receivers.